ello
i was wondering if anyone had any knowledge on whether there was any way to fit a 68 shell bb in a 73 frame?
ive been hunting for a nice 73/122 bottom bracket, but the only ones i can find are UN53s theres loads of nice 68 shell ones but not 73 so i was wondering if it was possible to use one a 68 with a bit of fannying around?
taa very muchly for any help!
mike

Although a 68mm bb can be used in a 73 mm shell, it places the equipement at two distinct disadvantages.

The first is that the cartridge unit is not supported fully in the shell cup, allowing for potential lateral and vertical play which will be recognized through the cranks as exagerrated movement. This movement can eventually lead to deformity of the shell cups.

Secondly, frames are built around the bb width. Often chainstays are placed farther outboard from the bicycle centerline with the larger 73mm bb to allow for more tire clearance or a less extreme bend enroute to the rear dropouts. When using a bb spindle that is appropriately sized for a 68mm shell, your crank arms and chainrings will clear the right chainstay without issue. Place the same sized unit in a 73mm shell and you have reduced the intended clearance.

I would suggest taking a bit more time to find the correct unit rather than rig the 68mm to fit.

older un71 & un51 BBs had removeable cups (not shimano intended). using a vice the cup could be tapped away from the main body. the main body was the same between 68&73 with different width outer threaded shells press fit over the body. newer shimano BBs dont allow this.

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